RE: iMount
I have an iMount stand for three screens.
I cant advise on the combination that you'll need to support seven monitors, but I will suggest looking at an eight screen system - Yes it'll cost you the price of another monitor, but I guess the cost of the additional graphics card support would be marginal.
[I use Matrox g200; picked them up from eBay for circa 30GBP - they support 4 screens each and fit into a PCI slot rather that PCIe. There is a "stuttering" effect when clicking and dragging etc, but they are only thirty quid. And, importantly for me, all I had to do was plug them in, no farting around with drivers etc...}
I suggest this as then you can simply buy two 4x4 stands rather than engineering some archaich system. Furthermore - and don't take this as any judgement of your trading - two 4x4 stands are a much more liquid asset to sell if it all goes tits up; this is business after all.
One thing I will highlight is the monitor size capabilities...
I am using 3 x LG 19" monitors. When I first ordered the stand, I did not order the extention arms as the website stated I would not need them. However, when I mounted the monitors alongside one another, they didn't fit. I emailed iMount (I never got hold of them on the phone) and told them of my situation. They sent out arm extenders immediately and I got them the next day (bear in mind I'm in London too), after which everything works fine.
As an aside, you do get what you pay for. Yes they are cheap, but they are a little flimsy to go with it. If you are considering clamping them to a desk, you will experience some "leaning" and wobble forward of the arm, and they don't quite line up perfectly. Washers from B&Q will sort it. Or bolt them into the wall (unless your in offices, how often are you going to move a 6+ setup around????).
As I think of it, I did have an issue with paying for the bloody thing. I tried to pay via Paypal AND their website C.C. system, but neither worked first time. Anyway; they didn't charge me twice, they seem like a good bunch of guys - and if you go to their website (as opposed to eBay) you can get delivery free. I bought mine in Jan as part of a home office setup, so the info is pretty recent.
If you are interested i will take some photo's of the arms "in action", so you can see what you're getting.
At the end of the day, with seven (or eight) screens you must accept there will be some tweaking to do to get them just how you want them. Perhaps you will have to do more tweaking with iMount stands than others - but I've finished tweaking mine and I'm happy to say that they do their job well.
